Recently, light-emitting display devices for uses in mobile devices are increasingly strongly desired to have higher definition and consume less power. Examples of display devices for uses in mobile devices are liquid crystal display devices (LCDs), display devices using elements for spontaneously emitting light, for example, organic light-emitting diode (OLED) display devices, electronic paper display devices, and the like.
Organic light-emitting diode display devices and electronic paper display devices do not require a backlight unit or a polarization plate, which is required in liquid crystal display devices. Therefore, the organic light-emitting display devices and the electronic paper display devices can be merely formed of thin films, and thus can be made flexible. In addition, such display devices do not use a glass substrate, and therefore are lightweight and are not easily breakable. For these reasons, organic light-emitting diode display devices attract a lot of attention. Especially, a compact organic light-emitting diode display device having high precision is now desired.
In a production process of a display device, a circuit for driving inspection (driving inspection circuit) located in the display device is inspected (tested). For the testing, a pad for testing (testing pad) that is located in a peripheral area of a display panel and is connected to the circuit via a line for testing (testing line) is supplied with an external signal by probing. For modularization of the panels formed on a substrate, the substrate and a counter substrate are bonded together via a sealing material. In addition, external elements such as LSI chips, FPCs and the like are mounted on a pad for an external terminal (external terminal pad) connected to a driving circuit of the panel via a line for an external terminal (external terminal line). In a conventional display device, as described in, for example, Japanese Laid-Open Patent Publication 2006-330711, the testing pad and the external terminal pad are located adjacent to each other.
In a display device obtained by reducing the size of the display device described in Japanese Laid-Open Patent Publication 2006-330711, the sizes of these pads are reduced and the distance between the pads is also shortened, which makes the layout difficult. In addition, in the case where, as in a flexible circuit board, a member easily deformable by an external pressure provided by probing or the like is located below the testing pad, the pad and also an area in the vicinity of the pad are deformed by probing. This also deforms the external terminal pad located adjacent to the testing pad, which adversely influences the mounting of the external elements during a step of modularization. In addition, since the distance between the pads is shortened, a highly precise positional alignment mechanism is required for probing performed for testing. Since a high alignment precision is required, the alignment needs a longer time and thus the productivity is decreased.